1. Field of the Invention
This invention relates to a variable valve mechanism which opens and closes intake and/or exhaust valve(s) of an internal combustion engine at a timing corresponding to an operation state of the engine and an internal combustion engine equipped with such a variable valve mechanism and, in particular, to a variable valve mechanism utilizing a nonuniform coupling which can increase or decrease, during one rotation, the rotational speed inputted therein and output thus changed rotational speed and an internal combustion engine equipped with such a variable valve mechanism.
2. Description of Background Art
A reciprocating internal combustion engine (hereinafter referred to as engine) is equipped with intake and exhaust valves (which are hereinafter collectively referred to as engine valves or simply as valves). Since such a valve is driven in a valve lift state corresponding to the form of a cam or its rotational phase, the opening/closing timing of the valve and the opening period thereof (quantity, by unit of rotational angle of a crank, indicating a period in which the valve is open) also corresponds to the form of the cam or its rotational phase.
Meanwhile, for the intake and exhaust valves attached to the engine, optimal opening/closing timing and opening period vary depending on states of load and speed of the engine. Therefore proposed are various kinds of so-called variable valve timing apparatus (variable valve mechanisms) which can alter the opening/closing timing and opening period of such a valve.
In particular, developed is a technique in which a nonuniform coupling employing an eccentric mechanism is inserted between a cam and a camshaft, whereas the camside rotation axis is set at a position eccentric to the camshaft-side rotation axis, and the eccentric state of the cam-side rotation axis in the eccentric mechanism (i.e., axial center position of the camshaft-side rotation axis) is adjusted so that, while the camshaft makes one rotation, the cam increases or decreases its rotational speed or changes its phase, thus allowing the opening/closing timing and opening period of the valve to be regulated.
Such a technique using a nonuniform coupling is proposed, for example, in Japanese Patent Publication No. SHO 47-20654, Japanese Patent Application Laid-Open (Kokai) Nos. HEI 3-168309, HEI 4-183905, and HEI 6-10630, and the like.
In each of the variable valve mechanisms for the internal combustion engine utilizing a nonuniform coupling, such as those mentioned above, a turning force is transmitted to the cam via the nonuniform coupling. When the turning force is thus transmitted, such turning force is transmitted through complex transmission paths between the camshaft-side rotating member and the cam-side rotating member that rotate with rotating axial centers eccentric to each other in the nonuniform coupling by way of several kinds of members such as connecting members (e.g., pin elements) which transmit the turning force while radially sliding.
In particular, in a connecting member such as pin element, when the turning force is transmitted between the camshaft-side rotating member and the cam-side rotating member, the rotation driving force from the camshaft side and the valve-driving reaction force from the cam side act on rotating directions opposite to each other. Consequently, at a part provided with the connecting member, a large load synthesized by these rotation driving force and valve-driving reaction force is generated in a direction orthogonal to the axial line, whereby a sliding surface of the rotating system also bears a large load, thus increasing friction at this sliding surface.
On the other hand, between the camshaft-side rotation axis and cam-side rotation axis, a member (axis-supporting member) for holding the cam-side rotation axis in a predetermined eccentric state with respect to the camshaft-side rotation axis is necessary. In order to adjust the opening/closing timing and opening period of the valve, this axis-supporting member is required to change its position so as to alter the eccentric state (position of the eccentric axial center in general) of the cam-side rotation axis relative to the camshaft-side rotation axis.
Though such an axis-supporting member rotates or swings within a predetermined range upon adjustment of the opening/closing timing and opening period of the valve, it is basically a member on the fixed side and does not rotate together with the cam-side rotation axis or camshaft-side rotation axis. Namely, the axis-supporting member bears the above-mentioned large friction at least at its sliding surface with respect to the cam-side rotation axis.
Such friction is deemed to greatly influence, when the axis-supporting member is rotated or swung in order to adjust the valve characteristics (opening/closing timing and opening period), the response of the axis-supporting member and an actuator for rotating or swinging the axis-supporting member.